Sclerotherapy is a cosmetic medical procedure used to treat varicose veins and spider veins. A tiny needle is used to inject a solution  directly into the vein. The solution irritates the lining of the vessel, causing it to swell and stick together, and the blood to clot. Overtime, the body will absorb the treated vein. Mild discomfort may occur, and a cramping sensation may be felt for 1 to 2 minutes when larger veins are injected. The number of veins injected in one session is variable, depending on the size and location of the veins, and the patient's overall medical condition. Anywhere from one to several sclerotherapy sessions may be needed for any vein region. Medically prescribed support hose and/or bandages may need to be worn for several days to several weeks to assist in resolution of the veins. In general, spider veins respond to treatment in 3 to 6 weeks, and larger veins respond in 3 to 4 months.